The invention relates to a process for steeping corn or sorghum kernels in the production of starch and other products. As a matter of convenience only, the process will be described hereafter as applied to corn although equally applicable to sorghum.
Steeping of corn kernels is the first step in the processing of corn to obtain different product fractions like germs, proteins and starch. In this first step the hard corn kernels are steeped to soften them. The kernels absorb water and they swell. At the same time water-soluble substances are leached out of the corn and pass into the steepwater. The temperature of the steepwater is generally in the range 40.degree.-55.degree. C. The sulfur dioxide which is usually present in an amount of about 0.2%, by weight, breaks the cell wall structure and prevents the growth of microorganisms during steeping. The steeping process lasts about 48 hours. All subsequent steps, in which the different product fractions are obtained, are much shorter. The corn steep liquor (CSL) obtained is concentrated by evaporation. The product obtained will mainly be used as animal feed but is also utilized as a nutrient in microbial fermentations. The swollen kernels are further separated into germ, fiber, starch and protein fractions in succeeding steps.
As is common in many other plant seeds, phytic acid, the hexaphosphate ester of myoinositol, is present in the corn kernels. Phytic acid usually appears in the form of calcium and magnesium salts, which, as a class, are called phytin. A large part of the phosphorus present in plants is stored in these compounds. In the steeping process most of the phytic acid reports to the CSL. It forms an undesirable component therein for at least the reasons enumerated below:
(1) The phytic acid in CSL tends to deposit a sludge with PA1 (2) When used as a nutrient in microbial fermentations, CSL is diluted and the pH is raised to 4-5. When this medium is sterilized, the phytic acid forms a precipitate coating on the inner surface of the fermenter. This precipitate is hard to scrub off afterwards and it also interferes with the purification of the fermentation end products. PA1 (3) When CSL is used as animal feed the phytic acid present gives the following problems. Phytic acid, because it interacts with multivalent metal ions, interferes with the assimilation of various metals in the body of animals (and humans). This may lead to deficiency disorders. Phytic acid also inhibits the activity of various enzymes in the body such as pepsin. Besides, the phosphate present in the phytic acid is not available for monogastric animals, because they only can digest phytic acid to a restricted extent. PA1 (a) steeping corn or sorghum kernels in warm water containing sulfur dioxide in the presence of an enzyme preparation comprising one or more phytin-degrading enzymes, PA1 (b) separating the steepwater from the kernels and concentrating it, PA1 (c) milling the kernels coarsely and separating and dewatering germs, PA1 (d) fine-milling the kernels, separating fibers from starch and protein, and dewatering the fiber fraction, and PA1 (e) separating starch and protein from each other, concentrating the protein fraction and drying and/or converting the starch fraction.
proteins and metal ions. This has caused problems in
concentrating by evaporation and in transporting and storing the CSL.
There have been proposals for removing phytic acid from the CSL. Thus, U.S. Pat. No. 2,515,157 describes a process for the treatment of CSL to obtain an improved nutrient for antibiotic fermentations. In this process the phytic acid is removed by adding an aluminum ion-furnishing compound to the CSL at low pH, heating and separating the aluminum phytate formed.
U.S. Pat. No. 2,712,516 describes a similar process wherein phytate is precipitated as its calcium salt.
The processes described in the above-mentioned U.S. patents are performed following the steeping process. Therefore, an additional step is required for removing phytic acid.